1. Field of the Invention
The present invention relates generally to vibratory finishing machines, and, more particularly, to a novel and improved bowl-type vibratory finishing machine.
2. Prior Art
Many surface finishing operations such as deburring, burnishing, descaling, cleaning and the like can be conducted expeditiously in a vibratory finishing machine. Such a machine includes a movably mounted receptacle and a drive system for vibrating the receptacle. Workpieces to be finished are loaded into the receptacle together with finishing media. A finishing action is imparted to the workpieces by vibrating the receptacle so that the mixture of workpieces and media is effectively maintained in a fluid or mobile state with smaller components of the mixture dispersed between large components for impact. Impulse forces imparted to the mixture not only cause repeated impacts among its components but also cause the mixture to churn in a predictable manner as a finishing process is carried out.
Two basic types of vibratory finishing machines are in common use. One type employs an elongate, substantially horizontally disposed receptacle which is vibrated by eccentrics rotating about horizontal axes paralleling the length of the receptacle. This first type of machine is known in the art as a "tub-type machine" or simply "tub machine," and its receptacle is commonly called a "tub." Another type uses a substantially annular receptacle which is vibrated by rotating one or more eccentrics about a vertical "center axis" located centrally of the receptacle when the receptacle is at rest. This latter type of machine is known in the art as a "bowl-type machine" or simply "bowl machine," and its receptacle is commonly called a "bowl." While tub and bowl machines have many similar characteristics, they are sufficiently different in arrangement and operation that one will frequently offer advantages over the other in solving a particular finishing problem. The present invention relates to bowl-type machines.
During operation of a bowl machine, the bowl vibrates in gyratory movements about a node point located somewhere along the machine's center axis. This gyratory movement subjects the bowl's contents to a complex of vertical, radial and tangential impulse components which are intended to effect a uniform dispersion of the smaller components of the workpiece and media mixture among the large components of the mixture for impact. The resultant impulses are so oriented and timed as to cause both circumferential precession of the mixture and rotation of the mixture in essentially radiating vertical planes.
Those skilled in the art maintain different and conflicting theories on where the node point should be located along the center axis. Some maintain that the node point should be located within or near a horizontal plane which includes the center of gravity of the bowl's contents. This arrangement effectively minimizes horizontal impulse components imparted to the bowl's contents and maximizes the vertical components. Others maintain that a node point location slightly below the bottom of the bowl's chamber is desirable since it gives something of a mix of vertical, horizontal and tangential components. Still others advocate higher and lower node point locations.
Those skilled in the art similarly advance different and conflicting theories on the number of eccentrics which should be used to vibrate the bowl, the locations of the eccentrics, and the relative orientations of the eccentrics where more than one is used. Still other theories obtain on how and where a drive motor should connect with the eccentrics.
Factors such as node point location, the number, location and arrangement of eccentrics, and features of the drive motor connection all intertwine to determine such other factors as:
(a) the simplicity or complexity of the machine; PA1 (b) the ease with which the machine can be serviced and such parts as bearings replaced; PA1 (c) the longevity of service which can be expected from the machine; PA1 (d) the sensitivity of the machine to different bowl loadings, i.e. whether it can handle a wide range of large and small, heavy and light loads; and PA1 (e) the type of vibratory movement which is imparted to the bowl, which, in turn, determines such things as:
(i) the type of circulation movement which will be executed by a mixture of media and workpieces in the bowl; PA2 (ii) the direction and rate of precession of the mixture; and PA2 (iii) the effectiveness of the resulting finishing action in terms of quality and time required to carry it out.
Previous proposals made in an effort to optimize these factors have resulted in machines which are relatively complex and difficult to service. The need for frequent bearing replacement has been a continuing problem, and the construction of many such machines has made bearing replacement difficult. Most bowl machines are quite sensitive to changes in bowl loading and operate effectively only in a relatively narrow loading range.
The invention described in the referenced Bowl Machine Suspension System Patents addresses the foregoing and other problems of the prior art. These patents describe bowl-type machines having a combination of features that are unique to the industry. These machines are of simple, relatively inexpensive construction. They have a relatively simple but rugged base structure, equally simple and rugged bowl structures, and utilize highly durable elastomeric mounts to support their bowl structures on their base structures.
Significant features of the inventions described in the Bowl Machine Suspension System Patents lie in their novel arrangement of elastomeric mounts. Each mount has one portion secured to a base structure and another portion secured to a bowl structure. The one and another portions define an axis for each mount.
In accordance with one of the Bowl Machine Suspension System Patents, the mounts are arranged such that their axes intersect at a common point along the center axis of the bowl. The machine's drive system is arranged to vibrate the bowl about a node point which coincides with this common point. The arrangement of mounts assures that forces imposed on the mounts by movements of the bowl structure load the mounts in shear, i.e. in planes normal to their axes. When arranged and loaded in this manner, the mounts tend to resiliently oppose movements of the bowl structure in any mode other than about the desired node point. As a result, the machine is found to be substantially less sensitive to variations in receptacle loading than are other, previously proposed bowl-type machines. A single machine can, for example, handle bowl load volumes within as large a range as 2 cubic feet to 6 cubic feet, and is operable to impart a good finishing action to the load anywhere within this very broad range.
In accordance with the other of the Bowl Machine Suspension System Patents, certain of the mounts are arranged such that their axes intersect at a common point along the machine's center axis above the node point, while others of the mounts are arranged such that their axes intersect at another common point along the machine's center axis below the node point. Still other mounts may be provided with their axes arranged such that they intersect the machine's center axis at the node point. Such an arrangement of elastomeric mounts assists in stabilizing node point location and in reducing the sensitivity of the machine to variations in bowl loading. Additionally, the mounts are loaded principally in shear by the dead weight of the bowl structure and its contents. The invention described in the present patent differs in that it utilizes some mounts which are not loaded solely in shear by vibratory movements of the bowl structure.
Bowl machine proposals prior to the inventions described in the referenced Bowl Machine Suspension System Patents do not address the problem of stabilizing actual node point location. It is believed that the tendency of node point location to vary with changes in bowl loading explains, at least in part, the difficulty prior proposals have encountered in providing machines that will handle a wide range of bowl loadings. If the actual location of the node point about which a bowl structure moves is displaced from the location for which the machine was designed, the machine operates inefficiently, if at all, and causes excessive wearing of drive and suspension system components.
Another problem of bowl-type machines relates to the linings used to cover the inner surface of the bowl structure. Whereas tub machines have elongate tubs of relatively simple configuration, bowl machines have relatively complex, toroidal-shaped bowls. Molding a replaceable, torus-shaped liner is difficult and expensive. Many bowl machine proposals use a cast-in-situ liner which requires extensive machine disassembly and replacement of the bowl shell when a liner is to be changed. The expense and effort and lengthy downtime required to replace bowl machine liners is, in fact, one of the major drawbacks which influence purchasers to buy a tub-type machine when a bowl-type machine might better serve their needs. Accordingly, it is important in any acceptable bowl-type machine that a relatively easily formed, easily replaceable liner be used.
The eccentric drive systems utilized in the referenced Bowl Machine Suspension System Patents provides for the removable mounting of a plurality of eccentric weight members. If the radial orientation of the weight members relative to the shaft required changing, the mounting arrangement required a mechanical repositioning of a weight support arm relative to the drive shaft. Desirably, the drive system would permit relatively easy repositioning of a weight relative to the drive shaft.
Yet another consideration of bowl-type machines relates to the technique by which the bowl structure is unloaded. Certain prior proposals have called for the use of a removably positioned ramp to direct a mixture of finishing media and workpieces onto a screen which overlies the bowl. The screen effects separation of the finishing media from the workpieces. As the workpieces travel across the screen for discharge, the media drops through the screen back into the bowl.
The Unloading System Patent describes and claims an effective solution to the problem of unloading the bowl. In the Unloading System Patent, the floor of the bowl is provided with a mound-shaped formation having a substantially horizontally extending top surface. A foldable ramp member is insertable into and removable from the bowl. One end of the ramp member is engageable with the mound-shaped formation and the other end of the ramp member is engageable with a channel-defining structure including a screen across which workpieces and media travel. The ramp member cooperates with the mound-shaped formation to direct finishing media and finished workpieces from the floor of the bowl upwardly into the channel. Although the Unloading System Patent describes an effective solution to the problem, it is desired to improve even more upon the simplicity and ease of operation of the assembly.